Problem:
A certain forecasting method would procuse the forecast show in the bottom row for the last four months, as compared to actual demand in the same four months as shown in the middle row. What is the MAD (Mean Absolute deviation)?
Month -4 -3 -2 -1
Actual Demand 105 100 95 90
Forecast 102 101 110 111
a. 102.5
b. 97
c. 10
d. 4
Please explain.